Electric circuit interrupter



Sept. 19, 1950 T. R. coGGEsHALL ELECTRIC CIRCUIT INTERRUPTER Filed July19, 1946 lllllllllllllll LI..

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Patented Sept. 19, 1950 ELECTRIC CIRCUIT INTERRUPTER Thellwell R.Coggeshall, Balal Cynwyd, Pa., assignor to General Electric Company, acorporation of New York Application July 19, 1946, Serial No. 684,813

1 Claim. l

My invention relates to electric circuit interrupters for high voltagecircuits, and particularly to high speed circuit breakers of the liquidblast type for opening high voltage alternating current power circuitswithin a few half cycles.

More specifically my invention is a further development and animprovement upon the multi-break interrupter disclosed in U. S. Patent2,164,175 granted on an application filed by E J. Frank and assigned tothe same assignee as the present application.

In this type of interrupter. the movable contact structure draws aplurality of arcs in series simultaneously within av substantiallyenclosed casing which is immersed in a tank of insulating liquid such asoil, some of the series arcs having no immediate venting means so thatthey generate lpressure :areas within the confines of the casing whichare effective to blast streams of extinguishing liquid through expulsionports positioned opposite the other series arcs in the interruptingcircuit. The ported series arcs accordingly are extinguished by theblasts of oil that are motivated by pressure generated by the unventedseries arcs so that the circuit is interrupted prior to the subsequentestablishment of an isolating gap, the latter being effected by theseparation of a movable contact arranged external to the interruptercasing, but within the enclosing tank. The very effective abovedescribedinterrupting process, whereby an larc that is drawn opposite anexpulsion port within an oil confining chamber is extinguished by theblast caused by a pressure established adjacent to the arc, is generallyreferred to and recognized as oil blast action.

In order that circuit breakers of this oil blast type may satisfactorilyconform to modern high speed standards for which 3 cycle totalinterrupting time for 60 cycle alternating current is demanded, it isnecessary that the actual arcing or interrupting contact parting time beaccomplished in one and a half cycles or less. To make such high speedspossible it is necessary that the moving contact structure be made aslight as possible consistent with strength, while at the same time,reducing such structure to a simplicity that insures reliability ofoperation with consistently fast opening speeds.

It is therefore an object of my invention to provide a multibreakinterrupter having an improved movable contact structure capable ofopening at high speed.

It is a further object of my invention to provide a multi-breakinterrupter of simple design having a minimum number of component partsof light weight which are economical to manufacture and assemble, andreadily accessible for maintenance.

The advantages and further aspects of my invention will become apparentfrom the following description referring to the accompanying dnawing,and the features of novelty which chiaracterize my invention will bepointed out with particularity in the claims annexed to and formlng apart of this specification.

In the drawing, Fig. 1 thereof is a sectional view through the axis of amulti-break liquid interrupter which embodies the features of myinvention, while Fig. 2 is an enlarged view of the lower guide bearingsituated in the throat of the interrupter.

Fig. 1 illustrates a single interrupter element I of a single pole tanktype oil circuit breaker, the latter of which comprises a pair of suchinterrupters which depend flxedly from the top cover (not shown) of anenclosing tank 2 by means of a pair of symmetrically inclined conductorbushings, one of which is indicated by I. The pair of interrupters I areimmersed well below the oil level indicated toward the top of tank 2 andIare electrically connected in series when the lift rod I is in theupper or closed position as shown, and in which |position the conductingswitch blade 5 interconnects the'conducting structures within theinterrupters I, thereby completing a closed circuit through the breakerunit from the external or line terminal (not shown) of the bushing 3 tothe corresponding external line terminal of the opposite bushing. In atriple pole circuit breaker, as is well understood in the art, three ofthe above-described single pole breaker units would be arranged inspaced relationship and a common operating mechanism would be providedfor lowering or naising the lift rods 4 in unison for effecting a,circuit opening or closing operation respectively in the three phases.

When the breaker is tripped to open, the lift rod l and its switch blade5 are moved downwardly at high speed. During the initial part of thisopening movement, internal members respond automatically to draw andextinguish a series of arcs within the interrupters I as will bedescribed later, and continued downward movement of the blade 5 thenestablishes a pair of isolating gaps between the blade rod contacts 6and the interrupters I. The length of these gaps and the spacing of theinterrupters I within the oil filled tank 2 are such as to preclude thepossibility of electrical breakdown from bushing to bushing under anyvoltage conditions that might arise while the breaker remains in theopen circuit condition.

The interrupter I comprises a cylindrical casing 'l composed of amechanically strong laminated insulating material which is substantiallyclosed at its upper end by a conducting metallic adapter casting 8electrically connected to the bushing stud 8, and is closed at its lowerend by a ring-like conducting metallic member III to which is bolted theconducting metallic throat or guide member II. For withstanding internalpressures the adapter 8 and ring-like member I0 are each secured to thecasing 1 by a plurality of headless screws I2 radially disposed aroundthe cylindrical Wall of the casing.

Because it is unsound to cut threads in the walls of a bonded laminatedinsulating tube such as that constituting the casing 1, it heretoforehas been thought necessary to secure end wall members wedgingly to thecasing by expensive clamping means involving large abutting flanges onthe end members which overhang the casing wall such as is illustrated,for example, in the aforesaid Frank patent. In the interrupter of myinvention, l. dispense with such massive and complex structure andemploy instead the comparatively small diameter above-mentioned endmembers 8 and III which are machined to fit snugly into the recessivebores in the ends of casing 1 as clearly shown by the drawing. Tofurther reduce weight, I prefer to make these end members of a lightconductive metal such as aluminum alloy. The screws I2 which anchorthese end members to the casing wall each comprise a short headless studhaving a suitable hexagon or square countersunk recess at one end forapplying a wrench thereto and a tapered screw thread, preferably astandard pipe thread, at the other end. End members 8 and III each areprovided with several circumferentially spaced pipe tapped holes forreceiving the screws I2, while the casing 1 is provided withsmooth-walled holes which register with the tapped holes for receivingthe body of screws I2. By providing tapered threads for the screws I2,it is possible to enter the several screws in their respective tappedholes, prior to tightening, despite slight manufacturing variations inaxial alignment between the plain and tapped holes in the casing walland the end members respectively; also, when tightened, the screws I2are rendered virtually shakeproof due to the strong inherent wedgingeffect of the tapered threads. From the foregoing description, it willbe understood that the screws I2 serve rather as large diameter dowelswhich resist in shear the internal pressures of the casing exertedagainst the end walls thereof; and by locating screws I2 a short safedistance from the ends of the casing as shown. there is no danger of thescrew bodies tearing through to the casing ends as a result of theseinternal pressures.

For electrostatically shielding the lower conducting parts ofinterrupter I, a sheet metal open-ended hood I3 may be provided. Asillustrated by the drawing, this shield conveniently is secured byscrews to the guide member II through access holes in the wall of casing1; also the hood is notched out on the inner side in way of thereciprocable blade 5.

For the purpose of forming a plurality of breaks in series within thecasing 1, contact structure mounted for limited movement is disposedtherein comprising plural contact bridging members Il, which areresiliently mounted about a central axial member I5 of strong insulatingmaterial such' as compressed and cured laminated wood, having a reducedcylindrical guide .portion I6 which extends above the members shortsquare-sectioned body at its upper end and which is threaded at itslower end for uniting to it a light flanged contact I1 which abuttinglycooperates with the rod Contact 5 for establishing the f vlating gap,already referred to, subsequent to e interrupting process within thecasing. Preferably, I provide a frusto-conical depression in theunderside of the contact I1 as shown, thereby providing guiding meansfor centering the rod contact 6 as the latter abuttingly engages theformer during the closing operation. Concentrically disposed about thetensioned axial member I5 is a series of suitable insulating spacers andwashers secured in compressive relationship between the lower shoulderof the above-mentioned square-sectioned body of member I5 and theshoulder of flanged butt contact I1. Accordingly, it is clearlyobservable from the drawing that the movable element of the contactstructure within casing 1 comprises the axial member I5, the lower buttcontact I1 and the various component parts carried thereby, includingthe two similar bridging contacts I4. This movable element is guided foraxial reciprocable movement within the casing, both at its upper end byvirtue of guide portion I6 sliding within the bearing 3| of adapter 8,and at its lower end by spacer I8 sliding within the bearing 32 of guidemember Il. It will be evident that when the blade 5 moves down to effecta circuit opening operation, the movable element of each interrupterwill follow in abutting relationship to rod contacts 6 under the bias ofopening spring I9 until arrested by the engagement of washer 20 againsta stack of shock-absorbent washers shown lying upon the inner surface ofthe throat guide member I I. A suitable wipe distance is afforded eachof the movable contacts Il relative to the movable element by means of ashoulder formed by washer 2|, while a compression spring 22 below eachcontact Il provides adequate contact pressure when in the closedcontinuous current carrying position.

In this embodiment of my invention, the fixed contact structure withinthe casing 1 comprises an upper conducting and contact member 2l, whichis mechanically and electrically connected to the adapter casting B, anintermediate conducting and contact member 24, and a lower conductingand contact member 25 which, as shown, may be an extension of thering-like member I0; these several conductor-contacts being secured asnecessary to the casing wall by insulated screws 26. It will be clearfrom the drawing that the current path through each closed interrupterfrom the bushing stud to the switch blade 5 is via adapter 8, upperconductor 23, upper bridging contact Il, intermediate conductor 24,lower bridging contact Il, lower conductor 25, throat guide member II,flexible conductors 21, butt contact I1 and rod contact 8. It will alsobe evident that during the opening movement, when the movable contactelement moves downwardly, four series arcs will be drawn from the nxedcontacts, one at each end of each of the two -bridging contacts Il. Suchan arrangement is known as a four-break interrupter, and it will beclear to those skilled in the art that a structure such as thatdescribed above might be adapted for a two-break or a six-breakinterrupter by providing a lesser or greater number of conductors andcontacts in accordance with the desired voltage rating of the particularcircuit breaker involved, Where conductor-contacts extend adjacent thepath of the arc, such as is the case for members 24 and 25, they may beshielded from the arc by protective insulating sheathings 28 and 29. Theabutting or wiping portions of the fixed and movable conductors andcontacts preferably are provided 5 with conventional arc resistant metalfacings as depicted in the drawing.

f the four series arcs drawn at the four breaks in accordance with thedownward opening movement of the movable contact element, two of theseare interrupting arcs which are elongated closely adjacent to anexpulsion port member l0 of arc resistant insulating material secured tothe side wall of the casing 1. These renewable port members may beprovided with a set of horizontal slots as shown, for arc splitting inknown manner, and which register with corresponding and larger openingsin the casing wall. The remaining two arcs, one drawn at the lefthandend of the upper bridging contact I4 and the other at the right end ofthe lower contact il, constitute the pressure generating arcs" forproducing the effective well-known oil blast action.

For producing the high opening speed of the movable contact element, Imake all parts as light as possible consistent with strength; forexample, the bridging contacts I4 are preferably made of high tensilealuminum alloy. Hitherto it has been usual to mount the external buttcontact such as I1 in resilient relationship with the movable elementrby the interposition of a strong pre-loaded spring so that during theclosing operation the impact of the movable blades isolating buttcontact upon the external butt contact of the interrupter will not betransmitted directly to the main movable element. A resilient connectionof this sort not only involves additional weight of the total movableelement but also requires a kind of articulated joint between the -buttcontact and the movable element such as that disclosed in theaforementioned Frank patent.

I have found that any such articulation can impede the fast openingspeed of the movable element especially when the latter reciprocates inguide bearings having small clearance for sliding iit; for if unbalancedpressures, magnetic forces, or other conditions in the casing causebending or buckling in the movalble element, which bending can beaggravated by articulation, it is possible for the guided portions ofthe movable element to misalign to the point of binding in theirotherwise free sliding t bearings; an illustration of such objectionablebinding conditions being ail'orded by Fig. 2` I obviate theabove-described dii'iiculty entirely; firstly, by directly coupling thebutt contact i1 to the movable element by means of the threads at thelower end of the axial member I5 as already described, therebyeliminating all articulation and much of the tendency toward bucklingfrom the movable element in addition to dispensing with the undesirablemass associated with the former resilient connection between buttcontact and movable element. By reducing the total mass of the movingelement, faster opening speeds are made possible, or lighter springs canbe used, while the closing impact is correspondingly ameliorated andrendered unobjectionable.

Secondly, for removing all tendency oi' the movablaelement to bind orjam in its guide bearings, I provide but a very short length ofcylindrical bearing surface both for the guiding portion 3| of theadapter 8 at the upper end of the interrupter and for the guidingportion 32 of the throat member Ii at the lower end. In this connection,it will be observed that, inasmuch as the diameter of the guided throatspacer il is made more than twice that of the upper guide rod Il, aneffective downward piston action is applied to the movable contactelement during interruption which assists in opening the contacts athigh speed, so that, for this reason, it is advantageous that theannular clearance of the lower guide bearing be held to a minimum inorder to take i'ull advantage of this piston action. By reducing theeffective length of the cylindrical bearing surface, I contrive to keepthe clearance small and at the same time prevent binding conditions aswill be most clearly understood by referring to Fig. 2 which shows anenlarged and somewhat exaggerated diagram illustrating the guided memberi8 inclined to the physical limit in the guide member il so that-binding or jamming in the [bearing would be likely to occur if it werepossible for the movable element to bend so excessively duringoperation. In the diagram, L represents the effective bearing length ofguide member il, A the maximum angle of deflection permitted by thebearing clearance and which latter, for all practical considerations,may be assumed to be the distance C. Hence, the relationship among L, Cand A may be expressed by the formula C-r-L: tangent A; or L=C+tangentA. Accordingly, after ascertaining a maximum value for the angle A andwhich is dependent upon the stiffness of, and the anticipated maximumsidewise forces acting upon, the contact carrying structure comprisingthe axial member I5, and having established an acceptaible minimumclearance C for the bearing, I determine the maximum bearing length Lfrom the above formula and which length, if reduced slightly, willprovide a guide bearing in which the guided member never will assume theobjectionable condition of binding as shown in Fig. 2. For example, inthe embodiment shown in Fig. l, the actual bearing length L is .25", andthe minimum clearance C is .01" so that, from the above formula, it isevident that the length L was predicated on a maximum angle of deectionA of somewhat more than two degrees; for the tangent of an angle 218' is.04, which is .Ola-.25: this predetermined angle being known to begreater than any likely to be produced under operating conditions of theinterrupter. Preferably, the short cylindrical bearing length L is madeto flare smoothly to a bell mouth at each end by providing a radius asat 3l. From the foregoing explanation, it will be understood that aguide bearing in accordance with my formula is one that inherently isdevoid of the axial guiding ability of conventional bearings havingcomparatively long bearing surfaces, and can be defined as one in whichthe eiective bearing length L is less than tan A C being the minimumtotal diametral clearance of the bearing, and A the maximum angle ofmisalignment at the bearing likely to be produced under the most severeconditions of bending in the movable contact element. It will lbeappreciated that binding conditions of the reciprocable movable contactelement in its guide bearings could also be eliminated Iby providing anntermediate supporting bearing thereby preventing the bowing whichproduces the binding, but in such an arrangement, the multiple bearingswould be dimcult to align, the additional center bearing would ibediillcult to install and additional length of the interrupter would benecessary. By using the simple inexpensive short bearings in accordancewith my invention, I tolerate and provide for the bending in the movableelement thereby achieving faster and more consistent opening speeds thanheretofore, for the only frictional resistance to the opening movementis that due to the virtual side thrust in the bearings caused byunbalanced sidewise forces within the interrupter casing 1. Another, butmore expensive, alternative within the purview of my invention might bethe substitution of a conventional spherical type self-aligning bearingat 3| and 32.

Thirdly, I reduce the above-mentioned frictional resistance in the guidebearings to a minimum by using for the guide spacer I8 insulatingmaterial which is known to have a low coeiiicient of friction withrespect to metals, especially where intermittent operation only isrequired. Such insulating materials are in the group comprisinglaminated fabrics impregnated with phenolic resin and which arevariously known to the trade as Textolite, Bakelite, etc. The axialmember I5, as stated earlier, is composed of compressed laminated woodwhich, also being treated and impregnated with phenolic resin, isincluded in this same low-friction category. For the same reason, Iprefer to make the spacers on which the bridging contacts I4 are mountedfrom Textolite, whereas the other cylindrical spacers and washersmounted on the member I5 may be of other mechanically strong insulatingmaterials such as fiber. By using this low-friction insulating materialin the manner set forth, I avoid the expense and electrical difiicultieswhich would be involved if sleeves of antifriction metal were fittedover the wearing surfaces of guide portion I6 and the guide spacer I8.Such metal to metal bearings are very objectionable in that sparking isproduced by differences in potential which results in the impairment bypitting of the sliding surfaces.

Severally and collectively then, the application of the threeabove-enumerated friction reducing devices makes possible the fast andconsistent opening speed which characterizes the interrupter of myinvention.

It will be observed from Fig. 1 that removal of the non-articulatedmovable contact element from the casing 'I is accomplished withoutdisturbing any of the fixed internal contact structure; by firstremoving the shield I3, then unfastening the throat guide member II fromthe ring casing I0, The movable element, complete with guide member I Iand the opening spring I9, then may be drawn downwardly during whichoperation a quarter turn brings the projecting ends of the bridgingcontacts into alignment with clearance grooves (not shown) in the ringcasting I0 thereby permitting complete removal of the movable elementfrom the casing for inspection or repair.

In view of the above detailed description and analysis, it is believedthat only the following brief review of the operation of the interrupteris necessary. Responsive to a tripping impulse, the blade 5, with themovable contacts within the interrupters I in follow-up engagement, isunlatched and moves downwardly at high speed vnder the acceleratinginfluence of springs I9 and 22. This spring actuated high speed openinf:movement is augmented by the piston effect due to the difference incross-sectional areas between the large diameter guided spacer I8 andthe small diameter guide rod I6 of the movable contact element. Also,high speed opening movement is attended by a minimum of friction due tothe short length guide bearing surfaces provided at II and I! whichindividually are incapable of axially guiding the reciprocating membersmoving therein under normal operating conditions.

In the initial opening movement, each contact Il separates from thefixed contact structure to draw a pair of arcs, one at each end of themoving contact. The interrupting arc of each pair is drawn from one endof contact I4 across the expulsion ports in the renewable port member30, while a pressure generating arc is established at the opposite endof contact Il. The resulting oil blast action within casing is effectiveto extinguish the interrupting arcs, whose products o! arcing are driventhrough the expulsion ports into the low pressure region in the tank 2,usually before the rod contacts 6 of the blade 5 separate from theircoacting isolating contacts I1. Continued downward movement of blade 5to its fully open position interposes adequately safe isolating gaps inthe breaker circuit. After interruption, the casings 1 refill with oilfrom the tank, oil flowing back through the expulsion ports, whileresidual gas may escape through suitable vents N in the top of thecasing.

It should be understood that my invention is not limited to specificdetails of construction and arrangement thereof herein illustrated, andthat changes and modifications may occur to one skilled in the artwithout departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

An arrangement for operating a. movable contact of an electric circuitbreaker comprising a slender longitudinally reciprocable insulatingcarrier structure operably related to a movable contact, said carrierstructure having a cylindrical portion of greater diameter at one endthan at the other end for aiding in moving the movable contact structureto the open position in response to pressure generated within thechamber during a circuit interrupting operation, and a fixed annularbearing disposed near the ends of said carrier structure and throughwhich the ends oi.' said carrier structure are slidable, said bearingshaving bearing surfacesof such longitudinal length with respect to thediametrical clearance distance between the ends of said carrierstructure and the cooperating bearing surfaces that said carrierstructure is free to bend within its maximum angle of bend withoutencountering guiding action by either of said bearings actingindividually.

T'HEILWEIL R. COGGESHALL.

REFERENCES CITED The following references are of record in the file o!this patent:

UNITED STATES PATENTS Number Name Date 791,548 Fisher June 6, 1905975,285 Robertson Nov. 8, 1910 1,021,746 Badeau Mar. 26, 1912 1,034,000Durfee July 30, 1912 1,487,087 Burnham Mar. 18, 1924 2,098,801 ErbenNov. 9, 1937 2,164,175 Frank June 27, 1939 2,185,719 Baker Jan. 2, 19402,199,607 Bakken May 7, 1940 2,250,566 Baker et al July 29, 19412,253,009 Baker Aug. 19, 1941

